La Nina conditions currently are present across the equatorial Pacific Ocean. Equatorial sea surface temperatures (SSTs) are below average across the central and eastern Pacific Ocean. The CPC velocity potential based and RMM MJO indices indicate an enhanced MJO signal from the Maritime Continent to the Western Pacific. Forecasts of the RMM-based MJO indices show a decrease in amplitude as the signal shifts eastward across Phase 6 and Phase 7 pattern (Western Pacific) over the next two weeks. The Week 3/4 temperature and precipitation outlooks rely primarily on dynamical model forecasts from the NCEP CFS, ECMWF and JMA operational ensemble prediction systems, as well as forecasts from the Subseasonal Experiment (SubX), a multi-model ensemble (MME) of experimental ensemble prediction systems. Consideration is also given to the possible evolution of the predicted circulation pattern for Week 2.

The various model guidance supporting the Week 3-4 outlook is in good agreement today, depicting troughs across the east-central Pacific to the Hawaiian Archipelago, and over the eastern CONUS, while a ridge is indicated over Alaska and near the west coast of North America. The CFS, ECMWF and JMA ensemble means depict above-normal 500-hPa heights over Alaska and the southeastern CONUS, while near to below-normal 500-hPa heights are indicated over most of the northern and western parts of the CONUS.

The forecast temperature pattern for Weeks 3-4 incorporates the objective blend of the CFS, ECMWF, and JMA model forecasts, as well as statistical guidance primarily from the multiple regression tool that leverages trends along with current ENSO and MJO conditions. Calibrated temperature forecasts from the individual models and multi-model combinations of these forecasts support an enhanced likelihood of above-normal temperatures over most of the western and southern CONUS, with the highest probabilities over Arizona and New Mexico. The predict trough and below-normal 500-hPa heights enhance the odds for near to below normal temperatures for much of the northeastern CONUS. The various forecast guidance was in very good agreement over Alaska, where there is a greater than 70 percent chance of above-normal temperatures for western parts of the state.

The precipitation outlook is likewise based on the objective dynamical guidance, which is broadly consistent with the forecast circulation pattern and, to lesser extent, the low-frequency La Nina footprint. The various guidance is in fairly good agreement on the precipitation outlook. Near to below-normal 500-hPa heights lead to increased odds for below-normal precipitation over parts of the Southwest, the Southern Rockies, the Southern Plains, and the Southeast. There is a slight tilt toward above-normal precipitation centered over Montana, where upslope precipitation may become more frequent as surface high pressure noses southward over the High Plains. The forecast trough over the eastern CONUS favors above-normal precipitation over parts of the Great Lakes, the Northeast, the Ohio Valley, the Tennessee Valley, and the Middle Atlantic. Below-normal precipitation is forecast over Alaska, consistent with dynamical model precipitation guidance from the CFS, ECMWF, and JMA.

The temperature forecast for Hawaii remains a bit uncertain with the CFS and ECMWF depicting very weak signed anomalies during the period. Dynamical model from CFS and JMA precipitation forecasts indicate increased probabilities of above-normal precipitation for Kahului and Honolulu during the Week 3-4 period.

Temperature

Precipitation

FCST

FCST

Hilo

EC

EC

Kahului

EC

A60

Honolulu

EC

A60

Lihue

EC

EC

Forecaster: Luke He

The next week 3-4 outlook will be issued on Friday, Dec 15, 2017

These outlooks are based on departures from the 1981-2010 base period

These are two category outlooks and differ from official current three category outlooks currently used for the monthly and seasonal forecasts.

The shading on the temperature map depicts the most favored category, either above-normal (A) or below-normal (B) with the solid lines giving the probability ( >50%) of this more likely category (above or below).

The shading on the precipitation map depicts the most favored category, either above-median (A) or below-median (B) with the solid lines giving the probability ( >50%) of this more likely category (above or below).

In areas where the likelihoods of 2-week mean temperatures and accumulated precipitation amounts are similar to climatological probabilities, equal chances (EC) is indicated.

As of May 19, 2017, the temperature outlook is operational, while the precipitation outlook is still experimental